As silicon microelectronics have made computation ever faster, cheaper, more accessible and more powerful, the development of microfluidic chips, which are feats of miniscule plumbing where more than a hundred cell cultures or other experiments can take place in a rubbery silicone integrated circuit the size of a quarter, could bring a similar revolution of automation to biological and medical research. Right now biological automation is in its infancy, that it's all about using large robots to push fluids around in the same way that computers in the early days were about big mainframes. It's expensive, bulky, and inflexible. The expense, inefficiency and high maintenance and space requirements of robotic automation systems present barriers to performing experiments. By contrast, microfluidic chips are inexpensive, stable and require little maintenance or space. They also need very small amounts of samples and chemical inputs to make experiments work, making them more efficient, less power consuming, and potentially cheaper to use. However, it is difficult to enable a specimen to be separate into a plurality of samples automatically and accurately for performing various tests thereupon in a microfluidic chip, since the physical attributes of the specimen are not quite the same in the micro world. It is noted that, at the human scale, surface tension is a force of little relevance compared to the force of gravity, however, in a miniaturized scale, the significance of gravity is reduced and the surface tension is a force to reckon with, moreover, not only the cohesion force of the micro fluidics is becoming significant, but also the influence of particle infiltration upon surface in contact with the micro fluidics should not be overlooked any more.
Hence, it is not a simple task to automate the quantification and separation of a specimen in a microfluidic chip. Please refer to FIG. 1, which shows the pressures required to be overcome for enabling a micro fluidics to flow through a microchannel of reducing diameters, illustrated in “Utilization of surface tension and wettability in the design and operation of microsensors”, Sensors and Actuators B71 (2000) 60-67, by P. G. Wapner, et al. In 2000, Wapner had disclosed that the flowing of a fluid in a microchannel is no longer significantly influenced by gravity, however, other parameters, such as surface tension, are becoming more significant with the decreasing of the diameter of the microchannel. As seen in FIG. 1, the flow resistance is increase with respect to the decrease of the diameter, so that the design of the microchannel must be changed accordingly.
Please refer to FIG. 2, which is a miniaturized microfluidic system disclosed in “Micromachined thermoelectrically driven cantilever structures for fluid jet system”, Proc. IEEE Micro Electro Mechanical System Workshop, MEMS'92, 1992, by C. Doring et al. The miniaturized microfluidic system shown in FIG. 2 is characterized in that: the flowing direction of a micro fluidics can be controlled by electrical signals and thus the controlling is facilitated by the operation of certain active devices such as micro valves. However, the aforesaid system is disadvantageous in that the active valves are additional and required for the operation of the microfluidic system.
Please refer to FIG. 3 and FIG. 4, which are diagrams illustrating a method for controlling the flowing direction of a micro fluidics, disclosed in J. Micromechanics and Microengineering, 11, 567, 2001 and 11, 654, 2001, by G. B. Lee et al. The aforesaid method is characterized in that the flowing direction of the micro fluidics can be controlled without the help of any valve device. However, the aforesaid method is disadvantageous in that the control of the flowing direction is driven by voltage.
Please refer to FIG. 5, which is a biomedical test disc disclosed by Marc J. Madou et al. The biomedical test disc of FIG. 5 is substantially a plastic disc having a plurality of microchannels formed thereon by a means of electroplating and press-molding, whereas the flowing of a micro fluidics is driven by the centrifugal force induced by a rotation platform carrying the test disc with respect to the cooperation of five passive valves fabricated in the microchannels. In addition, microfluidic devices, such as micromixers, are formed on the biomedical test disc. However, the aforesaid biomedical test disc is disadvantageous in that not only the structure of the test disc is complicated, but also additional valves are required for the operation of the biomedical test disc.
Please refer to FIG. 6, which is a disposable surface tension driven microfluidic biomedical test chip disclosed by F. G. Tseng et al. The biomedical test chip of FIG. 6 is substantially a substrate having a layer of SU-8 disposed thereon while forming microchannel in the SU-8 layer; wherein the microchannel is formed into a H-shaped structure with a hydrophilic inner wall made of a ploydimethylsilozane (PDMA) material. By the H-shaped microchannel, samples can be dispense to different sensors by the driven of surface tension. However, the aforesaid biomedical test chip is disadvantageous in that it is required to be processed by a plasma process for enabling the microchannel to have a hydrophilic inner wall.
Please refer to FIG. 7, which is schematic diagram showing the operation of an autonomous microfluidic capillary system disclosed by B. Michel. The autonomous microfluidic capillary system is adapted to be applied by an immunoassay chip, that it is substantially a formation of a plurality of microchannels of different aspect ratio while integrating the microchannel formation with micro devices, such as micro pump and micro valve, etc., so as to enable a micro fluidics to be separated and flow into each microchannels independent to each other and correspondent to the pressure and resistance exerted thereon by the structure of the corresponding microchannel. However, the aforesaid autonomous microfluidic capillary system is disadvantageous in that the structure of the corresponding immunoassay chip is complicated
With respect to the abovementioned prior-art disadvantages, the fabrication of microfluidic chip is complicated and costly. Therefore, it is in need of a low-cost, simple-structured and easy-to-implement platform or apparatus that is capable of enforcing an accurate and automatic quantification/separation operation upon a specimen.